At the present time, for the case of motion pictures, there are various techniques being used to permit the use of auxiliary (digital) audio sound sources for motion pictures. They require the preparation of a special film print which contains a unique marker code in place of the standard optical audio track. This special release print film, along with the digital audio recording and special playback equipment, is supplied to theaters for digital playback. Theaters with regular projectors must receive the standard film instead and cannot utilize the higher quality digital audio sound sources.
One reason why a unique marker code is required (rather than merely using the passage of time for synchronization) is that the motion picture film itself during its repeated handling and showing is subject to breakage and consequent film splicing. When the film is spliced, one or more frames of the film become lost at the splice depending upon whether the breakage was straight across the film or was a diagonal tear extending obliquely through more than one frame of the motion picture. This loss of one or more frames causes the motion picture and the sound track on the film to become shortened in physicial length. Thus, there is a sudden forward "jump" in the motion picture which momentarily loses synchronism with the sound track when the splice passes through the motion picture projector aperture. The synchronism is regained when the splice passes through the sound transducer. This momentary loss of synchronism is due to the physical film path distance between the projector aperture and the sound transducer as is conventional in motion picture projectors. The sound track is conventionally offset along the length of the film from the specific frames to which the sound track relates by an "offset distance" equal to the length of the normal film path distance in a projector between the optical aperture and the sound track transducer. The method and system of the present invention do not remove that momentary loss of synchronism caused by the interaction of a film splice with the physical film path distance between the optical aperture and the sound transducer.
There are other reasons why a marker code is used on the motion picture film for synchronization of an auxiliary sound source with the film. These other reasons include start-up, unexpected stoppage due to variety of possible causes and speed creepage of either the motion picture projector or of the auxiliary sound source.
In the case of video tape, there are many synchronizing systems available which use spacial marker coding systems. However, there is no method available for use with home type video cassettes.
With the continual development of improved consumer audio media, such as the compact disc (CD) and digital audio tape (R-DAT), and the marketing of audio processing systems for use with VCRs, the home viewer is seeking better quality sound, and the home viewer would like to enjoy this better quality sound with video viewing. This invention has direct application to this field of better quality sound to accompany video media.
In the case of editing video tape and film in post production, there are many synchronizing systems presently in use. However, there are numerous instances wherein a final or work print of a film or video production is made without synchronizing markers or codes. Additional editing, or remaking a better quality master, in which the various sources are synchronized to the work print, can be advantageously carried out by employing the invention.